Unit 2, L13 Hormonal Regulation of Body Water Flashcards
ADH is synthesized where
In the hypothalamus, in the paraventricular and supraoptic neurons
Where does ADH get released
It gets released from the posterior lobe of the pituitary
How does ADH spread throughout the body?
The posterior lobe of the pituitary is very close to blood vessels, so ADH is secreted directly into the blood stream, so the hormone can spread throughout the body
ADH’s production is dependent on the body sensing in 2 different regions
1) Baraoreceptors
2) Hypothalamus itself
ADH is released in response to what two things
1) Extracellular hyperosmolality
2) Volume depletion
Sensors of ADH
Hypothalamic osmoreceptors are the OVLT and the SFO, they stimulate production and ADH release
Aortic arch and carotid baroreceptors inhibit ADH release
Effector of ADH release
Exocytosis of ADH from terminal axons of supraoptic neurons and paraventricular neurons into blood of the posterior pituitary
Target of ADH release
Extracellular ADH receptors in distal tubules and collecting duct
Response to ADH release
Increased passive water reabsorption into renal medulla by causing insertion of aquaporins into the tubular epithelial cells
Other factors that affect ADH release
1) Ang II, it stimulates ADH release
2) ANP, it will inhibit ADH release
Healthy adults have an osmolarity of ______
275-290 mOsm/kg, but average is 280-285 mOsm/kg H2O
Above the level of 290 mOsm/kg H2O, what happens to levels of ADH
They rise sharply and linearly with plasma osmolality
How to the thirst receptors tell us to drink water
When the osmolality gets too high, usually around 298 mOsm/kg, it triggers the thirst receptors
What do AQP do
Mediate reabsorption of water, found on both basal and apical sides
Mechanism of insertion of AQP in the cell membrane
AVP will bind to the V2 receptors on the blood side, since its being released by the posterior pituitary into the blood supply. This is through the peritubular capillaries, and these will interface with the epithelial cells that make up the tubules. This will cause a signaling cascade of increasing cAMP to produce PKA. PKA will work 2 ways, first to put ready-made AQP into the membrane, and second, can stimulate activation of transcriptional factors that allow for more AQP to be synthesized and put into the membrane. AQP2 is on the lumenal side, on the urine side, which will allow water to go into the cell. There are also other AQP receptors on the basal side of the cell, towards the blood, to let the absorbed water to move back into the blood
Walk through the mechanism of dehydrating someone (ethically)
Depriving someone of H2O will cause an increase in plasma osmolarity. This will stimulate the osmoreceptors in the hypothalamus, causing ADH secretion. This will go into the blood supply, activating the AVP receptors and starts the downstream signaling cascade, resulting in AQP being inserted into the cell membrane. This causes the cells to facilitate water reabsorption in the distal part of the kidney. Urine osmolarity then goes up because you are extracting water but leaving salt behind, so you are concentrating the salt and urine volume goes down. This will decrease the plasma osmolarity towards normal. Additionally, there will be activation of the thirst receptors
